Rotational pulse generating circuit for motors

Abstract

A motor rotational pulse generating circuit for a motor is provided which generates a correct pulse signal even at an initial turning-on stage of the motor, by adjusting a filter cutoff frequency in response to motor rotational condition. The motor rotational pulse generating circuit includes a rotational pulse generation circuit 20 which generates ripple pulses based on a signal being inputted from the DC motor 1 , in which a ripple is superposed whose frequency is in proportion to a rotation number of the DC motor 1 . A filter 3 makes a cutoff frequency variable on the basis of a clock signal issued from a PLL circuit 6 . An oscillation frequency at an oscillator VCO 10 is determined by the ripple pulses and a motor rotation condition signal inputted by way of circuits 12 to 16 inclusive. A microcomputer 20 operates, when the motor is turned on, to cause the oscillator VCO 10 to issue a preliminary clock signal. The microcomputer 20 measures the oscillation frequency on the basis of the resultant preliminary clock signal to judge whether or not an initial cutoff frequency of the filter 3 is correct. If the result is negative, a switching circuit 17 is controlled in switching mode to adjust an attenuance of an attenuator 16 , thereby correcting the initial cutoff frequency.

What is claimed is:  
     
       1. A rotational pulse generating circuit for a motor, comprising: 
       a filter adapted and configured to eliminate noise from a signal inputted thereto, which signal is superposed with a ripple whose frequency is dependent on a rotation number of the motor, the filter being adapted and configured to make a cutoff frequency variable on the basis of an external signal;  
       a pulse shaper adapted and configured to convert an output signal of the filter to a pulse signal whose frequency is responsive to the rotation number of the motor;  
       a clock signal generator adapted and configured to generate a clock signal on the basis of the pulse signal and a rotational condition signal of the motor, the clock signal being fed to the filter for making the cutoff frequency thereof variable; and  
       a correction device adapted and configured to preliminarily oscillate the clock signal before turning on the motor, the correction device judging whether or not an initial cutoff frequency is adequate on the basis of the preliminarily oscillated clock signal, the correction device being configured to make the initial cutoff frequency adequate when the result of the judgment is found to be inadequate.  
     
     
       2. A rotational pulse generating circuit as set forth in  claim 1 , wherein the rotational condition signal is based on a motor rotational signal and a motor driving voltage signal, wherein the correction device stores a plurality of values of the cutoff frequency such that one of the values is an adequate value of the cutoff frequency for a given motor driving voltage, wherein the correction device determines an adequate value depending on the motor driving voltage represented by the motor driving voltage signal, and wherein the correction device judges whether or not the initial cutoff frequency is adequate by comparing the preliminary oscillated cutoff frequency to the determined adequate value. 
     
     
       3. A rotational pulse generating circuit as set forth is  claim 2 , wherein the correction device includes an attenuator and a controller adapted and configured to switch an attenuance of the attenuator, the attenuator being placed at an input side of the clock signal generator so that an attenuance of the rotational condition signal may be made variable. 
     
     
       4. A rotational pulse generating circuit as set forth in  claim 1 , wherein the correction device is adapted and configured to execute a judgment procedure whenever the motor is turned on. 
     
     
       5. A rotational pulse generating circuit as set forth in  claim 2 , wherein the correction device is adapted and configured to execute a judgment procedure whenever the motor is turned on. 
     
     
       6. A rotational pulse generating circuit as set fort: in  claim 3 , wherein the correction device is adapted and configured to execute a judgment procedure whenever the motor is turned on. 
     
     
       7. A rotational pulse generating circuit as set forth in  claim 1 , wherein the correction device is adapted and configured to execute the judgment procedure by preliminarily oscillating the clock signal at the clock signal generator on the basis of a motor driving voltage signal. 
     
     
       8. A rotational pulse generating circuit for a motor, comprising: 
       filter means for eliminating a noise from a first signal outputted by the motor on the basis of a cutoff frequency, the first signal including a ripple of whose frequency corresponds to a rotation number of the motor;  
       pulse shaping means for converting an output signal of the filter means to a pulse signal whose frequency corresponds to the rotation number of the motor;  
       generating means for generating a clock signal based on the pulse signal and the first signal, the generating means outputting the clock signal to the filter means so as to vary the cutoff frequency;  
       pre-oscillating means for pre-oscillating the clock signal at the generating means before the motor is energized; and  
       compensating means for compensating the pre-oscillated cutoff frequency to be an adequate frequency when the pre-oscillated cutoff frequency is an inadequate frequency.  
     
     
       9. A rotational pulse generating circuit as set forth in  claim 8 , wherein the first signal is based on a motor rotation signal and a motor driving voltage signal, and wherein the compensating means stores a plurality of adequate frequencies corresponding to various motor driving voltage signals so as to specify an adequate frequency based upon a motor driving voltage signal, and judges an adequacy of the pre-oscillated frequency in comparison with the specified adequate frequency. 
     
     
       10. A rotational pulse generating circuit as set forth in  claim 9 , wherein the compensating means comprises an attenuator located at an input side of the generating means so as to vary an attenuation magnitude of the first signal, and control means for switching the attenuation magnitude. 
     
     
       11. A method for generating a rotational pulse generating circuit for a motor, comprising the steps of: 
       eliminating a noise from a first signal outputted by the motor on the basis of a cutoff frequency using a filter, the first signal including a ripple of whose frequency corresponds to a rotation number of the motor;  
       converting an output signal of the filter to a pulse signal whose frequency corresponds to the rotation number of the motor;  
       generating a clock signal based on the pulse signal and the first signal, in a generator, the generator outputting the clock signal to the filter so as to vary the cutoff frequency;  
       pre-oscillating the clock signal at the generator before the motor is energized; and  
       compensating the pre-oscillated cutoff frequency to be an adequate frequency when the pre-oscillated cutoff frequency is an inadequate frequency.  
     
     
       12. The method as set forth in  claim 11 , wherein the first signal is based on a motor rotation signal and a motor driving voltage signal, including the steps of storing a plurality of adequate frequencies corresponding to various motor driving voltage signals so as to specify an adequate frequency based upon a motor driving voltage signal, and judging an adequacy of the pre-oscillated frequency in comparison with the specified adequate frequency. 
     
     
       13. The method as set forth in  claim 12 , wherein the compensating step comprises varying an attenuation magnitude of the first signal, and switching the attenuation magnitude.